With the growing capacity demand for optical fiber communications, optical crossconnects ("OXCs") with hundreds of ports are expected to become essential components of future optical transport networks within three to five years. This requirement in port count far outstrips the demonstrated capabilities of current deployable technology. Conventional mechanical switches suffer from large size, large element mass and slow switching time. On the other hand, guided-wave solid-state switches show limited expandability due to their high loss, high crosstalk and long device length.
Recently, free-space micromachined optical switching technology has been proposed as a means of building large optical crossconnects. This technology features the advantages of free-space interconnection, chiefly low loss and low crosstalk, while retaining the compactness and batch-fabrication economy of monolithic integration. Furthermore, the sub-millisecond switching times are well matched to the needs of OXCs in optical transport networks.
With the increasing capacity demand and complexity of optical networks, restoring network traffic promptly in the event of fiber failure becomes an important issue for network control and management. Optical crossconnects have been proposed as promising candidates for provisioning and restoration in optical networks at wavelength levels. In addition to protecting fiber failures, the optical crossconnect should also have protection schemes for itself so that its functionality will not be interrupted when one or more of its switching elements malfunctions.
Recent developments have focused on free-space micro-machined optical switches to achieve the optical performance and capacity requirement for optical crossconnects in multi-wavelength optical networks. The switch fabric includes micromachined free-rotating mirrors as switching elements. Backsides of the mirrors have also been used to achieve connection-symmetry in optical networks.